1. Field of the Invention
The present invention relates to a flame-retardant polycarbonate resin composition and its injection moldings. More precisely, it relates to a flame-retardant polycarbonate resin composition and its injection moldings, of which the impact resistance has been improved without lowering their flame retardancy and thermal stability, and which have good antistatic properties.
2. Description of the Related Art
As having the advantages of impact resistance, heat resistance and good electric properties, polycarbonate resins have many applications in various fields of, for example, office automation appliances, electric and electronic appliances, car parts and building materials. However, there are some problems with polycarbonate resins in that they require high molding and working temperatures and their melt fluidity is low. Therefore, they require relatively high molding temperatures. In particular, when various additives are added thereto, their thermal stability is often lowered, and, in addition, they could not often exhibit their good properties.
As a rule, polycarbonate resins are self-extinguishable. However, some of their applications to office automation appliances, electric and electronic appliances and others require high-level flame retardancy. To meet the requirement, various flame retardants are added to polycarbonate resins. As having high electric resistance like other ordinary plastics, polycarbonate resins are electrostatically charged with ease when rubbed or contacted with others. Charged polycarbonate resins are often problematic in that they receive electric shock when discharged or receive dust adhering thereto, by which their outward appearance is degraded. In particular, when moldings of polycarbonate resins for office automation appliances and other electric and electronic appliances such as those mentioned above are electrostatically charged, they cause IC errors. Given that situation, required are some measures for preventing polycarbonate resins from being electrostatically charged.
For preventing polycarbonate resins from being electrostatically charged, some methods have heretofore been tried. For example, water-absorbing hydrophilic compounds such as polyalkylene oxides, or antistatic agents are added to polycarbonate resins, or are applied to moldings of polycarbonate resins. However, as polycarbonate resins require high molding temperatures, such additives to them could not attain satisfactory antistatic effects. In particular, for flame-retardant polycarbonate resins to which are added some flame retardants, few concrete proposals have heretofore been made for making them have satisfactory antistatic properties without sacrificing the other characteristics intrinsic to them.
On the other hand, moldings for parts and housings for office automation appliances such as duplicators and facsimiles and for other electric and electronic appliances such as those mentioned above shall have a complicated shape with local projections or depressions, for example, having ribs or bosses therewith, and are required to be lightweight and thin-walled from the viewpoint of resources saving. Therefore, desired are polycarbonate resin compositions having increased melt fluidity, or that is, having increased injection moldability. Various polycarbonate resin compositions having increased moldability have heretofore been proposed, to which are added rubber-like polymer-modified styrenic resins in consideration of the physical properties such as impact resistance of the moldings of the compositions. However, no concrete method is known for improving the antistatic properties of polycarbonate resins.
On the other hand, compositions of polycarbonate resins to which are added styrene resins such as acrylonitrile-butadiene-styrene resins (ABS resins), acrylonitrile-styrene resins (AS resins) and the like are known as polymer alloys, and have many applications in the field of moldings as having good heat resistance and impact resistance. Of their applications, where such polycarbonate resin compositions are used for office automation appiances, electric and electronic appliances and others, they are required to have high flame retardancy of not lower than a predetermined level so as to ensure and increase the safety of their moldings.
To meet the requirements as above, various methods have heretofore been proposed. Concretely, JP-A 61-55145 discloses a thermoplastic resin composition comprising (A) an aromatic polycarbonate resin, (B) an ABS resin, (C) an AS resin, (D) a halogen compound, (E) a phosphate, and (F) a polytetrafluoroethylene component. JP-A 2-32154 discloses a molding polycarbonate composition with high flame retardancy and high impact resistance, comprising (A) an aromatic polycarbonate resin, (B) an ABS resin, (C) an AS resin, (D) a phosphate, and (E) a polytetrafluoroethylene component. JP-A 8-239565 discloses a polycarbonate resin composition comprising (A) an aromatic polycarbonate, (B) an impact-resistant polystyrene resin with rubber-like elasticity, (C) a halogen-free phosphate, (D) a core/shell-type grafted rubber-like elastomer, and (E) talc.
These are all to improve the melt fluidity and therefore the moldability of polycarbonates, and to improve the impact resistance and the flame retardancy of the moldings of polycarbonates. As having such improved properties, the polycarbonate compositions proposed are formed into various practicable moldings. However, in special fields of office automation appliances, electric and electronic appliances especially those for household use, etc., parts and housings of those appliances are required to be more lightweight and thin. In particular, their shape is being more complicated to have fine projections and depressions such as ribs and bosses therewith or have a lattice structure, so that they are applicable to any complicated and large-sized appliances.
Polycarbonate resin compositions containing any of ABS resins, rubber-modified polystyrenic resins (HIPS) and the like are problematic in that their thermal stability is poor, and, in addition, it is extremely difficult to make the compositions have good antistatic properties without interfering with their flame retardancy. In this connection, adding additives such as antioxidants to polycarbonate resins has been proposed, which, however, could not still solve the substantial problems with the resins.